1. Field of the Invention
The present invention relates to a belt conveying apparatus which uses an endless belt and is capable of adjusting a distortion of the belt with a simple mechanism.
2. Discussion of the Background
Conveying materials from one place to another using a belt is a popular technique that is widely used, for example, in image forming operations of an image forming apparatus, such as copying machines, printers, and so forth. More specifically, the technique is applied to, but not limited to, a transfer-sheet conveyer which conveys a transfer-sheet in the image forming operation of the image forming apparatus. Such a material conveying apparatus using an endless belt (hereinafter referred to as a belt driving apparatus) has drawbacks inherent to a rotating belt.
One problem associated with the rotating motion of the belt is that when the belt is required to regularly rotate along a predetermined line, the belt tends to shift laterally during a rotation. As a result, a transfer-sheet is conveyed to a displaced position.
Various methods for preventing the displacement of a belt have been proposed for belt driving apparatuses. For example, one method provides a course regulating member to the belt so as to regulate a course of the belt. Typically, the course regulating member is disposed with glue around an edge of the belt so as to move along the edge of a roller that drives the belt. A drawback of this method, however, is the structural brittleness of the member which must withstand a relatively large force that acts on the belt when it is out of alignment, which may cause the course regulating member to flake off, or to overstride the roller. The course regulating member may alternatively be mounted on an edge of the roller. In this case, however, the belt may receive an excessive pressure at an edge thereof, thereby being damaged by the course regulating member when the belt receives a relatively great force that acts on the misaligned belt.
Another method, for example, uses a roller which is capable of tilting so as to adjust the displacement of the belt. This method requires costly components such as a magnetic clutch or solenoid, or the like. Some other methods, for example, are described in Japanese Patent Laid-open Publication Nos. 5-14046/1993 and 4-121337/1992. The former uses a belt which is provided with a reinforcement on the edge of the belt. The latter uses a distortion detector that detects a distortion of the belt and a string that is wound and released, in accordance with belt distortion, so as to tilt a roller in a way to absorb the belt distortion. In this method, the belt may cause a relatively larger friction when overstriding the distortion detector, which results in a damage to the belt in a relatively short time period. In addition, this method suffers a difficulty in assembling parts, especially in installing the string into the belt driving apparatus. Furthermore, the string may erroneously become unwound when the belt driving apparatus is in operation.
Therefore, it is understood that there is no known belt driving apparatus which is capable of preventing belt distortion during rotation, eliminating the above-described problems, and preventing the damage to the belt edge due to the frictional wear.